1. Field of the Invention
This invention relates to an antenna, more particularly to a multifrequency inverted-F antenna for a portable electronic device.
2. Description of the Related Art
Wireless communication devices, such as cellular phones, notebook computers, electronic appliances, and the like, are normally installed with an antenna that serves as a medium for transmission and reception of electromagnetic signals. The antenna can be built outside or inside the devices. However, the latter (built-in type) are more attractive due to the tendency of folding and breaking associated with the former upon use.
FIG. 1 illustrates a conventional multifrequency Planar Inverted-F Antenna (PIFA) which includes a rectangular conductive radiating element 11 having opposite left and right ends, a rectangular conductive grounding element 12 that is vertically spaced apart from and that is electrically connected to the left end of the radiating element 11 through a conductive grounding leg 13, and a conductive signal feeding element 14 that is electrically connected to one side of the radiating element 11 at a feeding point between the left and right ends of the radiating element 11, that extends through an opening in the grounding element 12, and that is adapted to be electrically connected to a radio frequency transceiver (not shown). The length (L1) measured from the left end of the radiating element 11 to the feeding point is different from the length (L2) measured from the feeding point to the right end of the radiating element 11 so that two different frequency bands corresponding respectively to L1 and L2 (each length is about λ/4, wherein λ is the corresponding wavelength) can be emitted by the radiating element 11 when a signal is sent from the transceiver through the signal feeding element 14 to the radiating element 11.
FIG. 2 illustrates a conventional inverted-F antenna which is similar to the antenna shown in FIG. 1, except that the radiating element 11′ is in the form of a wire. The antenna of this type can only resonate in a single frequency band.
In view of the conventional inverted-F antennas, there is a need for a simpler structure and construction for the antennas that are capable of emitting and receiving multifrequency bands. Moreover, adjustment of the frequency bands through the input and output impedance is not possible for the conventional inverted-F antennas due to the fixed location of the signal feeding element 14 on the radiating element 11.